This invention is concerned with ratchet-type torque wrenches and more particularly with TAC pattern wrenches such as those covered by Federal Specification GGG-W-646 that have been available in the military supply system for years. TAC pattern wrench heads are available in many sizes and types but, in general, are characterized by a flat, elongated body with an annular ratchet wheel at one end for driving a socket, for example, and with a square drive opening at the other end for receiving the drive stud of a detachable handle. Different types of handles may be used with the same wrench heads, but the size of the square drive opening limits the choice of handles that can drive a given wrench head.
TAC pattern wrench heads have been found to be ideally suited for use with torque handles in tight quarters, the open-end head type being especially useful for torqueing tube fittings and the like. Originally, the torque ratings of the wrench heads and sockets were established in conjunction with bar deflection or dial type torque handles. The wrench heads and the sockets were made stronger than the highest torque value required for the mating torque hndles, because more torque may be required to break loose a fitting than to tighten it to a particular torque value. Nevertheless, the torqueing capabilities of the wrench heads and sockets were fairly well matched to the torque ratings of the mating torque handles. In recent years micrometer type torque handles have largely supplanted the bar deflection type, because they can be used in tight places where the bar deflection type cannot be used. However, because of the reduced torqueing capabilities of micrometer type handles, compared to a bar deflection handle of the same drive size, the torqueing capabilities of available TAC pattern wrench heads and sockets have not been employed to maximum advantage. For example, a TAC pattern wrench head with 1/4" square drive previously useful to a maximum torque value of 500 in.-lbs. can only be used for torqueing applications up to 150 in.-lbs. when driven by a 1/4" square drive micrometer type torque handle having a maximum torque rating of 150 in.-lbs. TAC pattern wrench heads with a 3/8" square drive previously useful to a maximum torque rating of 1200 in.-lbs. can only be used up to 750 in.-lbs., because the 3/8" square drive micrometer type torque handle has a maximum rating of 750 in.-lbs. Similar limitations are placed upon other TAC pattern wrench heads in torqueing applications.
Because TAC pattern wrenches have become standardized over a period of years, fundamental re-design of the wrench heads and/or the handles to permit full utilization of the torque ratings of the wrench heads and sockets in torqueing applications would render obsolete the thousands of wrenches now in service. A different solution to the problem was required.